The present invention relates to a cold cathode element for emitting electrons by application of an electric field to the element.
A hot cathode element and a cold cathode element are conventionally known as an electron-emitting element.
The hot cathode element is used in a field represented by a vacuum tube, but suffers from a problem that it is difficult to integrate, because heat is applied thereto. On the other hand, it is expected that the cold cathode element is applied to a flat panel display, a voltage-amplifying element, a high-frequency amplifying element and the like, as an element capable of being integrated, because no heat is used.
It is an object of the present invention to provide a cold cathode element of the above-described type, which has a high practicability and which is capable of emitting electrons sufficiently even at a low voltage applied.
To achieve the above object, according to the present invention, there is provided a cold cathode element which emits electrons by application of an electric field to the cold cathode element, and is formed of an amorphous carbon film, the refractive index n of a surface of the film being equal to or larger than 2.5.
The refractive index n is measured by a spectro-ellipsometry and assumes a value at a wavelength of 630 nm. In an amorphous carbon film, the refractive index n of the surface of which is set at a value equal to or larger than 2.5 as described above, the density of atoms forming the amorphous carbon film (which will be referred to as film-forming atoms hereinafter) is higher than that of a conventional diamond-like carbon (DLC) film and as a result, surplus electrons are produced in the amorphous carbon film, whereby the film is brought into a state in which it is difficult for such surplus electrons to be present in the solid. Therefore, the emitted electric field is reduced, whereby electrons can be emitted sufficiently even at a low voltage applied. However, if the refractive index n is smaller than 2.5, the density of the film-forming atoms is reduced. If n greater than 3.0, it is difficult to increase the density of the film-forming atoms due to a repulsive force between the carbon atoms. For this reason, the upper limit value of the refractive index n is set at 3.0 (n=3.0).
The amorphous carbon film can be easily used and can also be used as a material forming a surface film layer on a cold cathode element made of silicon (Si), for example, in order to enhance the performance of the cold cathode element.